Coal Preparation » General
A number of ACARP research projects are demonstrating useful outcomes from coal grain analysis (CGA), for example Project C18041.
Samples for CGA are prepared by the same method as for conventional petrographic analyses, namely by grinding to minus 1 mm topsize whilst aiming to keep the particles as coarse as possible.
The impact of resulting particle size distribution is negligible for conventional petrographic analysis since the analysis result only evaluates overall volumetric proportions of macerals and the overall reflectance distribution.
However, for CGA, the coal grain analysis is undertaken on each individual grain (particle). Therefore it is possible that 'harshness' of grind could impact on the CGA result. It is known that different laboratories use different equipment for preparing samples for petrographic analysis.
It was therefore considered prudent to investigate the repeatability and reproducibility of CGA by having several different laboratories prepare CGA analysis samples from replicate samples of each of several coal types.
The project has shown that the reproducibility of CGA is well within the acceptable values for conventional petrographics analysis, even after correcting to tighter standard reproducibility limits which apply after accounting for the larger number of point counts that are routinely possible with CGA.
The reproducibility data have been shown to be excellent, considering that this project included the errors associated with sample subdivision at 4 mm topsize and subsequent size reduction to 1 mm topsize. Those error components would not normally be taken into account.